• Proceedings of the KWS Conference
• /
• 2002.10a
• /
• pp.757-762
• /
• 2002

Many reports have been shown that the buoyancy, electromagnetic force, surface tension, and gas shear stress are the driving forces of weld pool circulation in arc welding. Among them, the surface tension of molten metal plays an important role in the flow in weld pool, which are clarified by the specially designed experiments with small particles as well as the numerical simulations. The surface tension is also related to the penetration in arc welding. Therefore, a quantitative evaluation of surface tension is demanded for the development of materials and arc process control. However, there are few available data published on the surface tension of molten metals, since it depends on the temperature and the composition of materials. In this study, a new method was proposed for the evaluation of surface tension and its temperature dependence, in which it is evaluated by the equilibrium condition of acting forces under a given surface geometry, especially back surface. When this method was applied to the water pool and to the back surface of molten pool in the stationary gas tungsten arc welding of thin plate, following results were obtained. In the evaluation of surface tension of water, it was shown that the back surface geometry was very sensitive to the evaluation of surface tension and the evaluated value coincided with the surface tension of water. In the measurement of molten pool in the stationary gas tungsten arc welding, it was also shown that the comparison between the surface tension and temperature distribution across the back surface gave the temperature dependent surface tension. Applying this method to the mild steel and stainless steel plates, the surface tension with negative gradient for temperature is obtained. The evaluated values are well matched with ones in the published papers.

• Journal of Industrial Convergence
• /
• v.20 no.10
• /
• pp.169-176
• /
• 2022

The purpose of this study is to verify the effect of positive psychological capital of fitness center trainers on emotional labor and job ability. For this purpose, as a convenient sampling method, 265 questionnaires were conducted by directly visiting a fitness center in the metropolitan area, and item analysis, validity analysis, reliability analysis, correlation analysis, and multiple regression analysis were applied to the collected data. As a result of the analysis, the following conclusions were obtained. First, in the relationship between positive psychological capital and emotional labor, it exerted a meaningful influence on hope and optimism in deep acting and superficial acting. Next, in the relationship between positive psychological capital and job competency, leadership ability is self-efficacy, hope, management ability is optimism, hope, counseling ability is hope, optimism, self-efficacy, PR ability is self-efficacy, optimism, and program operation ability is optimism. exerted a significant influence on elasticity. In relation to emotional labor and job competency, counseling ability exerted a significant influence only in deep acting, and in leadership ability, management ability, PR ability, and program operation ability, deep acting and surface acting exercised a significant influence. In the future, it is necessary to study the characteristics and properties of trainers as emotional labor and follow-up studies on improvement measures.

• 한국방재학회:학술대회논문집
• /
• 2008.02a
• /
• pp.541-544
• /
• 2008

Generally numerical analysis of tunnel lining, under dynamic loading condition, performed not considering pore pressure. But if tunnel excavated under the surface of water, such as bottom of the sea, the river bed, tunnel lining can take pore water pressure. It may be different from evaluated numerical analysis not considering pore pressure. Therefore tunnel design should consider effect of water pressure acting on tunnel lining.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.03a
• /
• pp.186-196
• /
• 2008

The dependence of the rheological properties of blood on shape, aggregation, and deformability of red blood cells (RBCs) has been investigated using hybrid systems by coupling fluid with solid models. We present a simple approach for simulating blood as a multi-component fluid, in which RBCs are modeled as droplets of acquired biconcave shape. We used lattice Boltzmann method (LBM) due to its excellent numerical stability as a simulation tool. The model enables us to control the droplet static shape by imposing non-isotropic surface tension force on the interface between the two components. The use of the proposed non-isotropic surface tension method is justified by the Norris hypothesis. This hypothesis states that the shape of the RBC is due to a non-uniform interfacial surface tension force acting on the RBC periphery. This force is caused by the unbalanced distribution of the lipid molecules on the surface of the RBC. We also used the same concept to investigate the dynamic shape change of the RBC while flowing through the microvasculature, and to explore the physics of the Fahraeus, and the Fahraeus-Lindqvist effects.

• 한국전산유체공학회:학술대회논문집
• /
• 2008.10a
• /
• pp.186-196
• /
• 2008

The dependence of the rheological properties of blood on shape, aggregation, and deformability of red blood cells (RBCs) has been investigated using hybrid systems by coupling fluid with solid models. We present a simple approach for simulating blood as a multi-component fluid, in which RBCs are modeled as droplets of acquired biconcave shape. We used lattice Boltzmann method (LBM) due to its excellent numerical stability as a simulation tool. The model enables us to control the droplet static shape by imposing non-isotropic surface tension force on the interface between the two components. The use of the proposed non-isotropic surface tension method is justified by the Norris hypothesis. This hypothesis states that the shape of the RBC is due to a non-uniform interfacial surface tension force acting on the RBC periphery. This force is caused by the unbalanced distribution of the lipid molecules on the surface of the RBC. We also used the same concept to investigate the dynamic shape change of the RBC while flowing through the microvasculature, and to explore the physics of the Fahraeus, and the Fahraeus-Lindqvist effects.

• Transactions of the Korean Society of Mechanical Engineers
• /
• v.9 no.4
• /
• pp.440-451
• /
• 1985

This study is concerned with the analysis of cutting force system acting on ball-nose end mill in three-dimensional surface machining process. Conical tipped circular cutting edge element model and free surface machining process types are proposed to apply oblique cutting theory, and then derived equations are used for numerical approach of cutting force curves by matrix method. This approach has a good agreement with experimental results both in magnitude and shape within the range of 15 percent, which was conformed on 6061-T6 aluminum workpiece having twofold curvatured surface. From the cutting load variation to edge location, it is confirmed that circular cutting edge shapes has a better cutting ability than that of straight and both have a singularity near a tool point. It is also verified that what kind of machining condition is recommendable for three-dimensional machining process in connection with deflection of the cutter to workpiece and tool point wearing or system stability.

• Bulletin of the Society of Naval Architects of Korea
• /
• v.23 no.2
• /
• pp.1-13
• /
• 1986

The nonlinear hydrodynamic forces acting on a two-dimensional circular cylinder, oscillating with large amplitude in the free surface, are calculated by using the Semi-Lagrangian Time-Step-ping Method used by O.M. Faltinsen. In present calculation the position and the potential value of free surface are calculated using the exact kinematic and dynamic free surface boundary condition. At each time step an integral equation is solved to obtain the value of potential and normal velocity along the boundaries, consisting of both the body surface and the free surface. Some effort was devoted to the elimination of instability arising in the range of high frequency. Numerical simulations were performed up to the 3rd or 4th period which seems to be enough for the transient effect to die out. Each harmonic component and time-mean force are obtained by the Fourier transform of forces in time domain. The results are compared with others' experimental and theoretical results. Particularly, the calculation shows the tendency that the acceleration-phase 1st-harmonic component(added mass) increases as the motion amplitude increases and a reverse tendency in the velocity-phase 1st-harmonic component(damping coefficient). The Yamashita's experimental result also shows the same tendency. In general, the present result show relatively good agreement with the Yamashita's experimental result except for the time-mean force.

• Journal of Korean Association for Spatial Structures
• /
• v.19 no.3
• /
• pp.41-50
• /
• 2019

The stone pagoda continued to be damaged by weathering and corrosion over time, and natural disasters such as earthquake are accelerating the destruction of cultural properties. Stone pagoda has discontinuous structure behavior and is very vulnerable to the seismic load acting in lateral direction. It is necessary to analyze various design variables as the contact surface characteristics play an important role in the dynamic behavior of stone pagodas. For this purpose, contact surface characteristics of stone pagoda can be classified according to surface roughness and filler type, and representative model is selected and structural modeling and analysis are performed using the discrete element method. Also, the seismic load according to the repetition period is calculated and the dynamic analysis is performed considering the discontinuous characteristics of the stone pagoda. Finally, the seismic behavior characteristics can be analyzed by the evaluation of stresses, displacements and structural safety.

• Journal of the Computational Structural Engineering Institute of Korea
• /
• v.29 no.2
• /
• pp.149-159
• /
• 2016

In this study, the solitary wave-induced tsunami force acting on an onshore bridges in coastal area was numerically modelled by means of TWOPM-3D based on Navier-Stokes solver and VOF method which can track free surface effectively. The validity of numerical analysis was verified by comparing the experimental tsunami bore force acting on vertical wall and column structure. In particular, the characteristics of tsunami force with the changing tsunami intensity were surveyed through numerical experiments. The availability of 3-dimensional numerical analysis was reviewed through the comparison between the existing numerical results and design criteria for each drag force coefficient by applying Morison equation considering only drag force. As reasonable and high-precision estimation method of tsunami force, it was suggested to apply the estimation method taking drag and inertial force into consideration at the same time.

• Korean Journal of Occupational Health Nursing
• /
• v.27 no.1
• /
• pp.25-35
• /
• 2018

Purpose: The purpose of this study was to figure out emotional labor, healthy lifestyle, needs for health services of flight attendants and the relationships among needs for health services according to various characteristics of flight attendants. Methods: The participants of this study were 140 flight attendants who work on major and low cost airlines. Data were collected through a questionnaire from 2017 .Jan.~2017. Feb. Data were subsequently analyzed using the SPSS 21 Program. Results: The score of emotional labor was 3.76 surface acting was 3.75 and deep acting was 3.77. The average of healthy lifestyle was 2.41, and the highest was 3.13 of personal relationship and the lowest was 1.91 of eating habits. There is a positive correlation between emotional labor-deep acting and healthy lifestyle. Flight attendants demand health services for physical exercise, stress and emotional labor management, healthy eating habits, emergency treatment, prevention of fatigue, cancer screening, sexual harassment prevention, sex education and etc. Conclusion: These results show that flight attendants need to various interventions for improving healthy lifestyle and reducing emotional labor. It is necessary to develop customized health promotion program suited to their job and general characteristics.